[Media Router] Remove the extension ID getter from MRMojoImpl

chrome/browser/media/router/mojo/media_router_mojo_impl.h

Index: chrome/browser/media/router/mojo/media_router_mojo_impl.h
diff --git a/chrome/browser/media/router/mojo/media_router_mojo_impl.h b/chrome/browser/media/router/mojo/media_router_mojo_impl.h
index b2ccaf563fe2ecf90dc759ce4689bc70e698345a..3a53511775508579493261267063e2e4dab6b622 100644
--- a/chrome/browser/media/router/mojo/media_router_mojo_impl.h
+++ b/chrome/browser/media/router/mojo/media_router_mojo_impl.h
@@ -114,9 +114,6 @@ class MediaRouterMojoImpl : public MediaRouterBase,
   scoped_refptr<MediaRouteController> GetRouteController(
       const MediaRoute::Id& route_id) override;
 
-  // TODO(crbug.com/597778): Remove this getter.
-  const std::string& media_route_provider_extension_id() const;
-
   void set_instance_id_for_test(const std::string& instance_id) {
     instance_id_ = instance_id;
   }
@@ -217,7 +214,7 @@ class MediaRouterMojoImpl : public MediaRouterBase,
 
   // Binds |this| to a Mojo interface request, so that clients can acquire a
   // handle to a MediaRouterMojoImpl instance via the Mojo service connector.
-  // Stores the ID of |extension| in |media_route_provider_extension_id_|.
+  // Passes the extension's ID to the event page request manager.
   void BindToMojoRequest(
       mojo::InterfaceRequest<mojom::MediaRouter> request,
       const extensions::Extension& extension);